Holder of the Two Leashes
May 3 2011, 02:52 PM
QUOTE (Toma B @ May 3 2011, 04:02 AM)
If there was no "upgrade" resolution should be about 1 m/pix this time because asteroid is 7 times closer!
It's not quite so simple, as this is not a passive observation but an active probe. The increase in resolution you are talking about could roughly be achieved by interferometric techniques (which might be used with the VLA, for instance), but with monostatic and bistatic (two antennas, such as Aricebo transmits and Goldstone receives) observations you have limitations due to time delay (ranging) and radio frequency (doppler shift) resolutions. Plus some minor limitations due to wavelengths (3.5 cm for Goldstone, 12 for Aricebo).
Goldstone will typically image an asteroid with about 0.1 microsecond bursts of radio waves. This results in a radio "pancake" about 30 meters thick. That is the relatively blunt instrument they use to image an object only 400 meters big. How they manage to process the return signal that comes back in a way that resolves detail smaller than that is beyond me, but they do manage it.
What you mainly get with this close approach is about 49 (7 squared) times more of the transmitted power being intercepted by the asteroid, and the same 49 times of the reflected signal being returned (the area of 2005 YU55 looks that much bigger this time), for a whopping gain of around 49 X 49 = 2401 (let's just say 2000-2500) times more of the transmitted signal being returned by the same antenna at the same power level this time around. A huge gain in signal-to-noise ratio.
But again it's more complicated than that. 2005 YU55 will be so
close this time that some sites, like Goldstone, won't be able to both transmit and receive due to the quick round trip time. At closest approach, they are only planning bistatic observations.
The link here provides a very detailed technical overview
of their plans at Goldstone.
I'm looking forward to this event for other reasons, hoping that through my telescope I can see this rock showing visible motion against the background stars, something I've only seen once before with 2002 NY40.